US6389138B1 - Method and apparatus for generating a complex scrambling code sequence - Google Patents

Method and apparatus for generating a complex scrambling code sequence Download PDF

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Publication number
US6389138B1
US6389138B1 US09/190,195 US19019598A US6389138B1 US 6389138 B1 US6389138 B1 US 6389138B1 US 19019598 A US19019598 A US 19019598A US 6389138 B1 US6389138 B1 US 6389138B1
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code sequence
complex
scrambling code
component
produce
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Quinn Li
Nallepilli S. Ramesh
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WSOU Investments LLC
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Lucent Technologies Inc
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Priority to US09/190,195 priority Critical patent/US6389138B1/en
Priority to CA002284330A priority patent/CA2284330C/en
Priority to AT99308692T priority patent/ATE219613T1/de
Priority to EP99308692A priority patent/EP1001568B1/en
Priority to DE69901870T priority patent/DE69901870T2/de
Priority to ES99308692T priority patent/ES2178868T3/es
Priority to AU58302/99A priority patent/AU764690B2/en
Priority to BR9906122-8A priority patent/BR9906122A/pt
Priority to CN99123466A priority patent/CN1115896C/zh
Priority to IDP991041A priority patent/ID23828A/id
Priority to KR1019990050144A priority patent/KR100669832B1/ko
Priority to JP32193399A priority patent/JP3559738B2/ja
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    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04J—MULTIPLEX COMMUNICATION
    • H04J13/00—Code division multiplex systems
    • H04J13/10—Code generation
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04B—TRANSMISSION
    • H04B1/00—Details of transmission systems, not covered by a single one of groups H04B3/00 - H04B13/00; Details of transmission systems not characterised by the medium used for transmission
    • H04B1/69—Spread spectrum techniques
    • H04B1/707—Spread spectrum techniques using direct sequence modulation

Definitions

  • This invention relates to wireless communications and, more particularly, to a system for generating a complex scrambling code sequence.
  • FIG. 1 depicts a schematic diagram of a portion of a typical wireless communications system 10 , which provides wireless communications service to a number of wireless units 12 a-c , such as mobile or fixed units, that are situated within a geographic region.
  • the heart of a typical wireless communications system is a Mobile Switching Center (“MSC”) 14 , which might be known also as a Wireless Switching Center (“WSC”) or a Mobile Telephone Switching Office (“MTSO”).
  • MSC Mobile Switching Center
  • WSC Wireless Switching Center
  • MTSO Mobile Telephone Switching Office
  • the Mobile Switching Center 14 is connected to a plurality of base stations, such as base stations 16 a-c , that are dispersed throughout the geographic area serviced by the system and to the local and long-distance telephone offices, such as local-office 18 , local-office 20 and toll-office 22 ).
  • the Mobile Switching Center 14 is responsible for, among other things, establishing and maintaining calls between the wireless units and calls between a wireless unit and a wireline unit (e.g., wireline unit 24 ), which wireline unit is connected to the Mobile Switching Center 14 via the local and/or long-distance networks.
  • a wireline unit e.g., wireline unit 24
  • each cell is schematically represented by one hexagon in a honeycomb pattern; in practice, however, each cell has an irregular shape that depends on the topography of the terrain surrounding the cell and other factors.
  • each cell contains a base station, which comprises the radios and antennas that the base station uses to communicate with the wireless units in that cell and also comprises the transmission equipment that the base station uses to communicate with Mobile Switching Center 14 .
  • base station 16 c which relays the information to Mobile Switching Center 14 .
  • Mobile Switching Center 14 Upon receipt of the information, and with the knowledge that it is intended for wireless unit 12 c , Mobile Switching Center 14 then returns the information back to base station 16 c , which relays the information, via radio, to wireless unit 12 c.
  • the information signal or baseband data sent between the base station 16 c and the mobile unit 12 c is multiplied by a spread spectrum signal.
  • a spread spectrum signal such as code-division multiple access (CDMA) systems, spread and/or scramble the baseband data information signal by multiplying the information signal with a spreading and/or scrambling code sequence (“scrambling code sequence”), such as a pseudo-noise (PN) code which is a binary sequence that appears random but can be reproduced by the intended receiving station.
  • PN pseudo-noise
  • the scrambling code sequence has the same pulse rate as the information signal, the product of the scrambling code sequence and the information signal is scrambled, and the spectrum is unchanged.
  • the scrambling code sequence has a faster pulse rate than the information signal, the product of the scrambling code sequence and the information signal has its spectrum spread in addition to being scrambled.
  • a single pulse of the scrambling code sequence is called a chip.
  • a scrambling code sequence generator 33 generates the scrambling code sequence, and a multiplier 34 multiplies the scrambling code sequence with the information signal D(t) to produce the wide band or spread spectrum information signal y(t).
  • Modulator 35 modulates the spread spectrum information signal onto a carrier signal, for example using quadrature modulation, after which the spread spectrum signal is transmitted to the receiver 31 .
  • a demodulator 36 demodulates the signal transmitted from the transmitter 30 to produce the spread spectrum information signal y(t).
  • the spread spectrum signal y(t) is multiplied by a multiplier 37 with a locally-generated version of the scrambling code sequence from a scrambling code generator 38 .
  • the multiplication with the correct scrambling code sequence de-spreads and/or de-scrambles the spread spectrum signal y(t) and restores the information signal D(t). Multiplying the spread spectrum signal y(t) from an undesired user with the scrambling code sequence results in a small amount of noise.
  • a decoder and deprocessing block 39 manipulates the information signal D(t) to obtain the original data.
  • each process in the transmitter 30 has a peer in the receiver 31 .
  • the data is being transmitted from the base station and received by the wireless unit.
  • the data is being sent over the reverse link.
  • the forward link and reverse link processes there are differences between the forward link and reverse link processes as well as differences in how the scrambling code sequence is generated.
  • FIG. 3 shows how the reverse link scrambling code sequence is generated for the TIA/EIA-95-B standard (“IS-95B”) using a (2 42 ⁇ 1) bit long code and a 2 15 bit complex short code.
  • a long code generator 40 generates a long code sequence which is the inner product of a 42-bit user mask 41 , which is uniquely assigned to each user, and a 42-bit long code vector which is the state of a long code generator engine 42 .
  • the long code generator engine 42 can be based on a shift register which maintains the long code vector or state of the shift register, and the mask 41 is used select bits from the long code vector which are exclusive-ord (for example, using AND gate arrangement 43 and mod 2 summer 44 ) to produce the long code sequence.
  • the long code is effectively time shifted a different amount for each user to produce the long code sequence.
  • the base station can identify the particular user.
  • the long code sequence is provided to a quadrature spreader 45 .
  • Quadrature spreading ensures that other user interference appears to have random phase and amplitude.
  • both the I spreading code sequence and the Q spreading code sequence are multiplied with the information signal D(t) to produce the I and Q spread spectrum signals y i (t) and y q (t) which are quadrature modulated and transmitted to the base station after being added together.
  • multipliers 48 a-b respectively multiply the information signal D(t) with the I spreading code sequence and the Q spreading code sequence to produce the in-phase spread spectrum signal y i (t) and the quadrature spread spectrum signal y q (t).
  • the quadrature spreader 45 multiplies the short complex code with the product of the information signal D(t) and the long code sequence.
  • the information signal signal D(t) can be multiplied with the long code sequence by a multiplier 49 before the quadrature spreader 45 in which case the information signal D(t) is scrambled by the quadrature spreader 45 and has already been spread by the multiplication with the long code sequence.
  • FIG. 4 shows an embodiment of the long code sequence generator 40 of FIG. 3 .
  • the long code sequence generator 40 includes a long code generator engine 42 , such as a linear feedback shift register with a 42 bit fixed generator polynomial 51 .
  • the current state of for the shift register is received by the mobile unit over the sync channel and loaded into the shift register as would be understood by one of skill in the art.
  • the shift register is then clocked, and the 42 bit code vector or current state of the shift register is applied to the AND gate arrangement 43 along with the user mask 41 .
  • the outputs of the AND gate arrangement 43 are applied to the modulo 2 summer 44 .
  • the modulo 2 summer 44 produces the long code sequence which is a time shifted version of the long code. The time offset being introduced by the user mask 41 .
  • the I and Q data signals D i (t) and D q (t) are scrambled by a complex scrambling code sequence by using a complex multiply operation.
  • the proposed CDMA systems use a complex long code sequence (whose I and Q components are two different real long codes) as the scrambling code sequence which is unique to each user.
  • Various techniques for generating the complex scrambling code sequence have been proposed.
  • FIG. 5 shows a complex scrambling code generator 50 using one long code sequence generator engine 52 and two 42-bit user masks, an I-mask 54 and a Q-mask 56 .
  • the current long code generator state 58 is received by the mobile unit over the sync channel and loaded into a 42-bit linear feedback shift register of the code generator engine 52 as described in FIG. 4 .
  • the code vector from the shift register of the code generator engine 52 is exclusive-ord with the I-mask 54 , for example using an AND gate arrangement 60 and a modulo 2 summer 62 , to produce the I long code sequence which is used as the I scrambling code sequence.
  • the code vector from the register of the generator engine 52 is also exclusive-ord with the Q-mask 56 , for example using an AND gate arrangement 64 and a modulo 2 summer 66 , to produce the Q long code sequence which is used as the Q scrambling code sequence.
  • the I mask 54 can be the IS-95B user mask 42 (FIG. 4 ), and the Q-mask 56 can be a permutation of a subset of the I-mask bits or a different set of fixed bits, for example inverting bit 32 of the I-mask 54 to get the Q-mask 56 .
  • This approach may produce self-interference problems because the relative time offset of the user's I and Q long code sequences may be small, thereby I and Q can cross interfere due to delay spread.
  • FIG. 6 shows another complex scrambling code sequence generator 70 which uses a user mask 72 and two long code generator engines, an I long code generator engine 74 and a Q long code generator engine 76 .
  • the I long code generator engine 74 receives the current state 78 from the sync channel as called for in IS-95B, and the current state is loaded into a 42-bit linear feedback shift register of the I code generator engine 72 as described in FIG. 4 .
  • the current state 78 is advanced by a certain number of chips (for example, 512 chips) as shown by block 80 and loaded into a 42-bit linear feedback shift register of the Q code generator engine 76 .
  • the code vector from the Q long code generator shift register is also exclusive-ord with the user mask 72 , for example using an AND gate arrangement 86 and a modulo 2 summer 88 , to produce the Q long code sequence which is used as the Q scrambling code sequence.
  • the user mask 72 can be the IS-95B user mask 42 (FIG. 4 ). This approach, however, increases the complexity of the circuitry and may produce mutual interference problems.
  • Mutual interference problems can arise because among users, I long code sequences are unique and Q long code sequences are unique, but one user's Q long code could be another user's I long code. Again, mutual interference problems can arise because there is no guaranteed delay between the I long code sequences (or Q long code sequences) of two different users.
  • FIG. 7 shows another complex scrambling code sequence generator 90 which uses a user mask 92 and two long code generator engines, an I long code generator engine 94 and a Q long code generator engine 96 .
  • the I long code generator engine 94 receives the current I generator state 98 from the sync channel as called for in IS-95B
  • the Q long code generator engine 96 receives the current Q generator state 100 from the sync channel.
  • the I state is loaded into a 42-bit linear feedback shift register of the I generator engine 94
  • the Q state is loaded into a 42-bit linear feedback shift register of the Q generator engine 96 .
  • the I and Q long code generator engines 94 and 96 have unique generator polynomials.
  • the I long code generator engine 94 uses the IS-95B generator polynomial, and the Q long code generator engine 96 can use the reciprocal polynomial of the IS-95B generator polynomial.
  • the code vector of the I long code generator engine 94 is exclusive-ord with the user mask 92 , for example using an AND gate arrangement 102 and a modulo 2 summer 104 , to produce the I long code sequence which is used as the I scrambling code sequence.
  • the code vector from the Q long code generator engine register is also exclusive-ord with the user mask 92 , for example using an AND gate arrangement 106 and a modulo 2 summer 108 , to produce the Q long code sequence which is used as the Q scrambling code sequence.
  • This approach reduces the interference problems but requires current I and Q states to be transmitted on the sync channel for both I and Q engine registers. Additionally, this system also does not guarantee the delay between the I long code sequences (or Q long code sequences) of two different users.
  • mapping between the user mask value to an offset value for the long code is very complicated.
  • a problem with the proposed schemes which employ only long code generators which are masked is the difficulty in guaranteeing the time difference between the I and/or Q scrambling code sequences of the same and/or different user's.
  • the present invention involves a complex spreading and/or scrambling code sequence (“scrambling code sequence”) generation system which uses a first complex code sequence having at least two components and a second complex code sequence having at least two components.
  • the components of the first complex code sequence are respectively mixed with the corresponding components of a second complex code sequence to generate the complex scrambling code sequence.
  • an offset between the components of the complex scrambling code sequence is achieved for the same and/or different users.
  • the complex spreading code sequence generation system can use a long code generator which produces a long code sequence produced from the inner product of a code vector and a user mask.
  • the long code sequence is provided to an I path and a Q path.
  • FIG. 2 shows a general block diagram of a transmitter and receiver pair in a spread spectrum communications system station architecture in the prior art
  • FIG. 3 shows a general block diagram of an embodiment of a current spreading code generation system
  • FIG. 4 shows an embodiment of a code sequence generator
  • FIG. 5 shows a proposed complex scrambling code generation system
  • FIG. 7 shows yet another proposed complex scrambling code generation system according to the principles of the present invention.
  • a Q mixer 140 mixes or multiplies the Q long code sequence with a second component of the complex short code sequence, such as a Q component of the short code sequence, to produce the Q component (Q scrambling code sequence) of the complex scrambling code sequence.
  • a delay could be used on the I path 132 alone or delays on both I and Q paths 132 and 134 to provide a relative delay between the I and Q long code sequences.
  • the delay between the I and Q long code sequences could be as small as one chip.
  • the complex scrambling code sequence is processed using a processing block 144 to alter the complex scrambling code sequence before performing a mixing or complex multiplication 142 with the data streams D i (t) and D q (t) in order to improve the peak power to average power ratio of the transmission.
  • the modulation scheme is effectively changed.
  • the processing block 144 could decimate the Q scrambling code by a factor of 2 and then multiply the resulting sequence by a repeating cover sequence of -1 and 1 and the I scrambling code sequence.
  • the resulting Q scrambling code sequence produced from the processing block 144 would be used in the complex multiplication of the complex scrambling code and the data streams D i (t) and D q (t).
  • the complex scrambling code would exhibit phase transitions which could reduce the peak to average power ratio.
  • the complex scrambling chip will be one of four quadrature phase shift keying (QPSK) symbols.
  • QPSK quadrature phase shift keying
  • the complex scrambling code is limited to s+/ ⁇ 90 degree phase shift from the previous complex scrambling chip.
  • the complex scrambling code sequence can be generated using a hybrid phase shift keying approach which is a hybrid combination of QPSK and binary phase shift keying (BPSK).
  • BPSK binary phase shift keying
  • the processing block 144 could alter both the I scrambling code sequence and/or the Q scrambling code sequence in different ways to effectively alter the modulation scheme or provide other desired operational characteristics.
  • the processing block 144 would not be performed and the complex scrambling code is directly provided to the complex multiplier 142 .
  • the “'” after Q scrambling code sequence denotes that the Q scrambling code sequence in this embodiment has been altered by the processing block 144 . Other embodiments are possible.
  • the system can be backward compatible with the TIA/EIA-95-B standard.
  • the system reduces the self-interference problem because the relative time offset between the user's I and Q scrambling codes will be sufficiently large (>than one period of the short code generators) due to the existence of the complex short code.
  • the mutual interference problem is reduced because the I and Q scrambling code sequences are unique among users, and one user's I code will be un-correlated with another user's Q code due to the use of different user masks and the different I and Q components of the complex short code sequence.
  • alternative configurations of the scrambling code sequence generation system are possible according to the principles of the present invention which omit and/or add components and/or use variations or portions of the described scrambling code generation system.
  • the above described embodiment is described as using a 42-bit user mask, 42-bit code vector and 15-bit short code sequences, but alternative mask, code vector, and code sequences are possible.
  • the code sequences are described as long and short, but alternative embodiments could produce the complex scrambling code using first and second complex code sequences with different relative lengths or equal lengths.
  • the complex scrambling code as well as the long and short code sequences are described in terms of two components (I and Q), but other embodiments can use additional components and/or different numbers of components which are combined in different fashions to enable various forms of modulation.
  • the long code generator engine is described as receiving the current state vector on the sync channel from the base station, but alternative schemes are possible where the current state vector is received from different sources.
  • the long code generator 122 is further described as using the code vector from the long code generator shift register to produce the long code sequence by taking an inner product using the AND gate arrangement 128 and modulo 2 summer 130 of the code vector 126 and the user mask 124 .
  • Alternative configurations are possible for generating the long code and short code sequences.
  • the complex scrambling code sequence generation system has been described using a particular configuration of distinct components, but it should be understood that the scrambling code generation system and portions thereof can be implemented in application specific integrated circuits, software-driven processing circuitry, firmware or other arrangements of discrete components as would be understood by one of ordinary skill in the art with the benefit of this disclosure. Although in the illustrative embodiment is shown with a particular circuitry, the system can use different components which together perform similar functions when compared to the circuitry shown. What has been described is merely illustrative of the application of the principles of the present invention. Those skilled in the art will readily recognize that these and various other modifications, arrangements and methods can be made to the present invention without strictly following the exemplary applications illustrated and described herein and without departing from the spirit and scope of the present invention.

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US09/190,195 1998-11-12 1998-11-12 Method and apparatus for generating a complex scrambling code sequence Expired - Lifetime US6389138B1 (en)

Priority Applications (12)

Application Number Priority Date Filing Date Title
US09/190,195 US6389138B1 (en) 1998-11-12 1998-11-12 Method and apparatus for generating a complex scrambling code sequence
CA002284330A CA2284330C (en) 1998-11-12 1999-09-29 Method and apparatus for generating a complex scrambling code sequence
AT99308692T ATE219613T1 (de) 1998-11-12 1999-11-02 Verfahren und vorrichtung zur erzeugung komplexer verschlüsselungskodesequenzen
EP99308692A EP1001568B1 (en) 1998-11-12 1999-11-02 Method and apparatus for generating a complex scrambling code sequence
DE69901870T DE69901870T2 (de) 1998-11-12 1999-11-02 Verfahren und Vorrichtung zur Erzeugung komplexer Verschlüsselungskodesequenzen
ES99308692T ES2178868T3 (es) 1998-11-12 1999-11-02 Metodo y dispositivo para generar una secuencia de codigo complejo de aleatorizacion.
AU58302/99A AU764690B2 (en) 1998-11-12 1999-11-05 Method and apparatus for generating a complex scrambling code sequence
BR9906122-8A BR9906122A (pt) 1998-11-12 1999-11-05 Método e aparelho para gerar uma sequência de código de embaralhamento complexo
CN99123466A CN1115896C (zh) 1998-11-12 1999-11-11 用于产生复数倒频代码序列的方法和设备
IDP991041A ID23828A (id) 1998-11-12 1999-11-11 Metode dan apparatus untuk membangkitkan suatu rangkaian kode pengacakan yang kompleks
KR1019990050144A KR100669832B1 (ko) 1998-11-12 1999-11-12 복소 스크램블링 코드 시퀀스를 발생하는 방법 및 장치
JP32193399A JP3559738B2 (ja) 1998-11-12 1999-11-12 コンプレクス・スクランブリング・コード・シーケンスを発生するための方法及び装置

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EP (1) EP1001568B1 (zh)
JP (1) JP3559738B2 (zh)
KR (1) KR100669832B1 (zh)
CN (1) CN1115896C (zh)
AT (1) ATE219613T1 (zh)
AU (1) AU764690B2 (zh)
BR (1) BR9906122A (zh)
CA (1) CA2284330C (zh)
DE (1) DE69901870T2 (zh)
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